This is a competing renewal proposal to investigate the differential diagnosis and longitudinal course of medical outpatients complaining of palpitations. We will also further examine the process of cardiac perception, the psychological factors which influence it, and the accurate awareness of cardiac arrhythmias. One hundred seventy-five consecutive patients referred for continuous ambulatory electrocardiographic (Holter) monitoring because of palpitations will be studied. We will assess cardiac symptoms, psychiatric diagnosis, life stress, beliefs about heart disease, somatization, and bodily absorption and amplification. Cardiac awareness, cardiac symptoms and cardiac activity will be assessed during Holter monitoring and exercise tolerance testing (ETT). The referring physicians will complete instruments rating their diagnostic impressions and clinical interventions. The patients' clinical course will then be followed over the ensuing 12 months with telephone interviews and in-person assessments. These data will permit us to describe and distinguish three subgroups of palpitation patients: those with panic disorder, in whom the symptom results from sympathetic nervous system arousal; those who are somatizing after a life event has caused them to suspect that they have heart disease, in whom the palpitation results from a cognitive misattribution of benign bodily sensation; and those with clinically significant arrhythmias, whose symptoms result from a major cardiac irregularity. These findings will be used to develop a clinical algorithm to aid in the differential diagnosis of palpitations and in identifying the patients most appropriate for Holter monitoring. We will also follow the patients' longitudinal course, determine the predictors of continued somatization and chronicity, and study their medical care by examining the referring physicians' diagnostic impressions and interventions. By comparing cardiac symptoms with concurrent cardiac activity during Holter monitoring and ETT, we will develop measures of cardiac awareness. We will then be able to describe inter-individual differences in cardiac awareness, examine several psychological factors which amplify or modulate awareness, and investigate the relationship between somatization and accuracy of symptom reporting. These findings will ultimately lead to improved cognitive and educational techniques to reassure and palliate palpitation patients, and to the early identification of patients who are unlikely to obtain symptomatic relief from antiarrhythmic therapy.